Manufacturing processes for automobiles have evolved from one that utilized primarily stamped and bent sheet metal pieces that were welded together through a MIG welding processes, i.e. a welding process in which a line of molten material is deposited by the welder in joining two pieces of metal together. Now, conventional automobile manufacturing processes incorporate in a greater degree hydroformed tubular members that are shaped to fit into the chassis of an automobile in a desired manner. The hydroformed members are particularly conducive to being welded through a spot-welding process, which involves the passage of electrical current between two electrodes to melt and join two pieces of metal placed between the electrodes. Spot-welding requires a frame design having appropriate access holes that is conducive to being manufactured using the spot-welding process. For example, if two tubular members are being spot-welded together, access to the adjoining walls of the two tubular members by the spot-welder electrodes must be provided. Other welding techniques, such as gas metal arc welding (GMAW), are also be utilized for welding tubular designs.
Hydroforming is a process by which a standard tubular stock member is placed into a form shaped to correspond to the particular member to be formed. A liquid is then introduced into the interior of the tubular stock and pressurized until the tubular stock expands to assume the shape defined by the configured form. The expanded and re-shaped tubular stock now has a substantially different shape. By forming cutouts and other access openings into the re-shaped tubular member, spot-welding electrodes can gain access to opposing adjacent sides to create a weld bond between juxtaposed members. In this manner, a frame, as an example, for an automobile can be created using in large part hydroformed tubular members. Once the hydroformed part is formed, attachment brackets are attached to the part to permit other components of the automobile to be mounted. Typically, these attachment brackets are welded to the hydroformed part by either a MIG or spot-welding process, whereupon the other components can then be bolted or welded to the attachment brackets.
The automotive body component hydroforming manufacturing process can start with a sheet metal tube, which can be provided in a large variety of sizes and shapes, as well as material thickness and grade. The sheet metal tube can be formed through a roll-forming process in which the sheet metal is rolled into the desired generally cylindrical shape and edge welded along the seam where one edge of the rolled sheet metal adjoins the opposing edge, thereby forming a tubular member that can be hydroformed into the desired shape and configuration. The shape of the hydroformed member is controlled by the shape of the die in which the tubular blank is placed before the blank is hydroformed into the desired shape. The interior of the hydroformed member is hollow, being formed from a tubular blank. Increased strength can be obtained by welding adjacent tubes together or by welding reinforcements to the hydroformed member.
Accordingly, it would be desirable to provide a hydroforming process by which multiple tubular cells can be formed in a single structural hydroformed component to provide integral internal reinforcements and increased structural strength with a given size and shape for the exterior of the hydroformed member.